Climate change lets invaders beat Alpine plants in mountain race

Saxifraga androsacea – ruling the mountaintop, but for how much longer?

Bob Gibbons/Alamy

By Andy Coghlan

As the climate warms up, invasive weeds are outpacing native Alpine plants to the tops of mountains, threatening them with extinction.

To avoid warming temperatures, Alpine plants can migrate to cooler habitats higher up mountains, but new research is showing that invasive species are beating them to it.

“We find that invasive species are responding to climate change far more quickly than the native ones,” says Matteo Dainese of the University of Würzburg in Germany, who led the team studying the phenomenon.

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Dainese and his colleagues discovered the unequal race to the summit after studying the distributions of 1300 plant species over 20 years – from 1989 to 2009 – on an Alpine mountain area around Mount Baldo in northeast Italy.

From 130,000 observations, they found that on average, the 126 non-native species were increasing their elevation range at twice the speed of the 1208 native species. During the study, the mean annual temperature rose by 1.2°C and the mean growing season temperature rose by 1.7°C.

Dainese and his colleagues found that the invasive species were more tolerant to warmth compared with the natives, and that they moved up the mountain faster. They spread their seeds more widely and their passage up the mountain was helped by roads whose verges provided convenient conduits toward the summit.

“A key finding of our study is that the combined effect of both global warming and human disturbance has accelerated species range expansion in an unprecedented way,” says co-author Lorenzo Marini, of the University of Padova in Italy. “Limiting growth of tourism, skiing developments and roads could be central to reducing these impacts.”

There is still time to save native plants. Only a few invasives have reached the highest elevations where native “snowbed” species such as Saxifraga androsacea are most vulnerable, because they can only move a fraction higher before running out of options.

But the invasives are catching up fast, and the biggest single threat at present is the South African ragwort (Senecio inaequidens), a type of daisy that arrived in exports of wool from South Africa.

“It’s a prolific seed producer, has vigorous growth and is toxic,” says Marini. “It’s quickly spreading in both disturbed and semi-natural habitats and is expected to have a pervasive effect on biodiversity.”